Related Stories

The ancient hunters of North America - accused of widespread extinctions upon their arrival 11,000 years ago - may have been innocent, says new U.S. research. But an Australian expert said the hunters are still not in the clear.

Led by Professor Donald Grayson of the University of Washington in Seattle and colleagues, the team analysed evidence from archaeological sites where humans and animals interacted. The work is published in the current issue of the Journal of World Prehistory.

They studied 75 locations in the United States and one in Canada that had mammal remains from the past 40,000 years. Of these, 14 sites had artefacts attributed to the Clovis people - among the first recorded inhabitants of the Americas - and animal remains so closely associated their relationship could not be accidental.

The Clovis people roamed North America between 10,800 and 11,500 years ago, leaving behind highly distinctive and deadly fluted spear points. They have been blamed for the extinction of 35 genera of mammals (or groups of species) that roamed North America in the Pleistocene, between 11,000 and two million years ago.

Mammoths were found at 12 of the 14 sites examined, and mastodon were found at the remaining two. There were no remains of the other 33 genera. The researchers concluded that the lack of any spearheads alongside the animal remains indicates the Clovis people were not hunting the animals, they cannot be held responsible for their extinction and therefore climate change was more likely to be responsible for the extinctions.

Clovis people not exonerated

But this reasoning is flawed said Dr Tim Flannery, director of the South Australian Museum in Adelaide, and author of The Future Eaters, which argues that Australia's megafauna were likely to have been wiped out by the arrival of human hunters on the continent some 40,000 years ago.

"There are no sites in Australia or New Zealand that place humans with the extinct animals," he told ABC Science Online. "But this would be expected if the extinction happened rapidly."

The absence of evidence placing human spears with animal remains is in itself not proof, but simply reflective of the small number of sites available to examine. Flannery has published research that looked at all the archaeological sites of Australian megafauna: there are only 28 sites in total. "That was all we could find," he said.

Australian megafauna - large land mammals that once dominated the continent - lived between 100,000 and 40,000 years ago, meaning there is an average of only one archaeological site for every 2,000 years. "If extinctions took 1,000 years, then the chances are very small of seeing an interaction," he said.

North America is replete with historical evidence of the rapid elimination of species, he added, citing the reduction in buffalo numbers in North America from 60 million head to just a few thousand over a single century. Passenger pigeons once numbered in the billions, but the species was completely wiped out within a century of Europeans arriving. "So extinctions can happen quite quickly," he added.

Climate change

Grayson sees it differently: "The bottom line is that we need to stop wasting our time looking at people as the cause of these extinctions," he said in a statement accompanying the scientific paper.

"We suspect the extinctions were driven by climate change. We have to tackle this species by species, one at a time, and look at the interaction of each species with the climate and vegetation on the ground," he added.

Flannery agrees that species-wide research should be done, but disagrees with Grayson's conclusion. He cited results published in 2002 of a series of radio-carbon datings which made it clear that in Cuba the sloth had survived until 7,000 years ago, despite being extinct elsewhere in the world for considerably longer.

If climate is the cause of this extinction, then we would need to find a climactic event that affected all other areas of the world except Cuba, Flannery argued.